Word problem

troublemaker676

Junior Member
Joined
Sep 1, 2005
Messages
84
Have a question about a tricky word problem,

At 5:00 am 1 person called two other people to tell them about a huge secret, completeting these calls took 5 minutes. These people called two other people. (Those calls took place at 5:05.) Those people continued the chain by calling two people each. Assuming no one was called twice and that each set of calls occurred exactly 5 minutes after the previous calls, how amny people were aware of the secret at 6:00 am?

Now I set up a table,

....................0.........1.........2..........3..........4..........................12
Time..........5:00......5:05.....5:10......5:15....5:20.......................6:00
# of people...3............7.........15.........31.......63.........................?
who know

Then i found the differences

Diff.....................4...........8...........16.........32
Diff.............................4...........8...........16
Diff.....................................2..........2

Now i know when the second differences are all the same you know they will fit into a quadratic model, which means you factor out the # of people numbers into 2 factors each, then you find the equation. I'm not sure how to find the equation if the third differences are all the same. Can someone show me the process from where i left off?
 
8 - 4 = 2?
16 - 8 = 2?

I'm a little troubled by your setup. It looks to me like you'll get 13 phone calls. That would be one extra.

This is an exponential model, not a quadratic.

How many people are informed during each of the 12 calling periods?

2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096

How many people know after each calling period?

3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191

Just for fun, add one (1) to each of these and see if it looks suspicious.
 
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